1. Field of the Invention.
Manufacture of crystalline aluminosilicate molecular sieve zeolites by admixing a flux with kaolin-type clay prior to calcination at an elevated temperature and subsequent aging of the calcined clay in caustic solution.
2. Description of the Prior Art.
It has heretofore been known to employ kaolin-type clays in synthesizing crystalline aluminosilicate zeolites as a result of treatment with caustic solution. Thus, U.S. Pat. No. 2,992,068 describes conversion of dehydrated kaolin clay by contact with a relatively concentrated caustic solution at low temperature into a type A zeolite. U.S. Pat. No. 3,037,843 describes treatment of a variety of clay minerals, particularly of the kaolin type, with caustic solution to yield a crystalline sodium aluminosilicate which is then treated with an acid to yield a "permutitic acid" which upon treatment with dilute alkali solution at an elevated temperature yields a crystalline aluminosilicate of the molecular sieve type. U.S. Pat. No. 3,114,603 describes a process which entails digesting an aqueous reactant mixture containing reactive kaolin at a temperature between about 20.degree.C. and about 55.degree.C. for at least 2 hours followed by crystallizing sodium zeolite A in the digested reactant mixture in the temperature range of about 75.degree.C. to about 100.degree.C. for at least 2 hours and recovering crystalline zeolite A as the product. U.S. Pat. No. 3,119,660 describes preparation of a molecular sieve-type crystalline aluminosilicate by contacting kaolin with an aqueous alkaline solution containing a water-soluble alkali metal salt. After a suitable period of digestion, crystallization occurs.
U.S. Pat. No. 3,338,672 describes a method for making a faujasite-type crystalline zeolite by reacting an aqueous sodium hydroxide solution with a mixture of amorphous dehydrated kaolin clays, which clays were produced by calcining kaolin clays at different temperature levels. U.S. Pat. No. 3,391,994 describes a method for producing faujasite-type zeolites by reacting sodium hydroxide solution with kaolin clay that had been calcined under conditions such that the clay had undergone the characteristic kaolin exotherm after it was dehydrated. U.S. Pat. No. 3,414,602 describes conversion of calcined kaolin by reaction with sodium hydroxide and tetramethylammonium hydroxide to yield zeolite N. U.S. Pat. No. 3,458,454 describes a procedure for providing a fluidizable cracking catalyst from calcined kaolin which is converted to pellets of precursor consisting of sodium faujasite in an amorphous matrix. Such pellets after conversion to particle size of less than 2 microns are admixed with sodium silicate, spray dried and finally exchanged by treatment with an ammonium salt.
U.S. Pat. No. 3,367,886 relates to zeolite molecular sieve-kaolin clay composites resulting from crystallizing the zeolite molecular sieve from sources of alkali metal oxide, aluminum oxide, silicon dioxide and water in the presence of raw crystalline kaolin clay while such sources and kaolin clay are intermittently mixed together and in the form of particles of the size and shape desired in the active contact masses. U.S. Pat. No. 3,367,887 describes the production of a catalyst base material obtained by hydrothermal treatment without dehydration of preformed masses of sodium hydroxide solution, calcined amorphous kaolin clays and raw crystalline kaolin clay in a manner such that the zeolite molecular sieve is produced by reaction of the caustic principally with the calcined amorphous clays in situ in the presence of the raw crystalline kaolin clay. U.S. Pat. No. 3,508,867 describes treatment of clays with sodium hydroxide or potassium hydroxide solution, preferably in admixture with a source of silica, followed by calcination at temperatures ranging from 230.degree.F. to 1600.degree.F. to yield a material which is crushed, dispersed in water and digested in the resulting alkaline solution to yield, upon crystallization, a crystalline aluminosilicate. U.S. Pat. No. 3,515,511 relates to preparation of faujasite by calcining raw kaolin at a temperature in the range of 965.degree.C. to 1095.degree.C. to yield a reactive kaolin which upon Differential Thermal Analysis at about 980.degree.C. exhibits an exotherm which is less than 15% of the DTA exotherm of raw kaolin and thereafter contacting the activated kaolin with sodium hydroxide solution. U.S. Pat. No. 3,515,681 and U.S. Pat. No. 3,515,682 describe techniques for transforming calcined kaolin into synthetic faujasite by alkaline aging in sodium hydroxide solution.